A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

Test solution: 10 mg per mL, in dioxane.

Mobile phase— Prepare a filtered and degassed mixture of methanol and water (4:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Transfer about 100 mg of desoxycorticosterone acetate to a 50-mL volumetric flask, add methanol to volume, and mix.

Standard preparation— Transfer about 12.5 mg of USP Desoxycorticosterone Pivalate RS, accurately weighed, to a 25-mL volumetric flask, add 20 mL of methanol, and mix. Add 2.5 mL of Internal standard solution, dilute with methanol to volume, and mix to obtain a solution having a known concentration of about 0.5 mg of USP Desoxycorticosterone Pivalate RS per mL.

Assay preparation— Transfer about 50 mg of Desoxycorticosterone Pivalate, accurately weighed, to a 100-mL volumetric flask, add 80 mL of methanol, and mix. Add 10.0 mL of Internal standard solution, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L7. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the analyte and internal standard peaks is not less than 2.0; and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 25 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.5 for desoxycorticosterone acetate and 1.0 for desoxycorticosterone pivalate. Calculate the quantity, in mg, of C26H38O4 in the portion of Desoxycorticosterone Pivalate taken by the formula: in which C is the concentration, in mg per mL, of USP Desoxycorticosterone Pivalate RS in the Standard preparation; and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.